Mix all ingredients together, just until combined. Fill cupcake tins about 2/3 full. Bake for 15-20 minutes, or until toothpick inserted in the middle comes out clean. Place pans on wire rack to cool for 10 minutes before removing cupcakes from pans.

While cupcakes cool, prepare peanut butter frosting.

Frosting:

1/2 C butter

1/2 C peanut butter

1 lb powdered sugar

1-3 tbsp. heavy whipping cream

Cream together butter and peanut butter. Slowly add powdered sugar and beat until smooth. Add heavy whipping cream, 1 tbsp. at a time, until desired consistency is reached.

Frost cupcakes and add sprinkles, if desired. Unwrap 24 Reese's Peanut Butter Cups (or more, if batter yielded extra cupcakes; mine often does). Add small swirl of frosting to each PB cup, then place on top of a frosted cupcake.